Image display apparatuses such as a plasma display panel (hereinafter referred to as PDP) use phosphors of 3 colors (red, green, and blue) each having a different persistence time. While blue phosphors have a persistence time of several microseconds as short as possible, red and green phosphors have a long persistence time of several tens of milliseconds until an amount of the phosphors is reduced to not more than 10% of the total.
First, a blur of a motion (hereinafter referred to as motion blur) in an image occurs due to persistence of the phosphors and movement of a line of sight.
Then, when an object displayed with emission of phosphors having different persistence times moves, color shift due to the motion blur occurs (hereinafter referred to as color shift).
A principle of the motion blur and the color shift will be hereinafter described.
First, integration on the retina will be described.
A human perceives light entering the human eyes by integrating an amount of the light incident on the retina, and the human senses the brightness and color based on the integration value through the sense of sight (hereinafter referred to as integration on the retina). The PDP uses the integration on the retina to generate tones by changing a light-emission time without changing brightness of the light.
FIG. 1 explanatorily shows integration on the retina for each color when an image signal of a white dot on a pixel is stationary. FIG. 1 shows that the motion blur does not occur when there is no change in a time distribution of emitted light from a PDP; in the integration on the retina; and in the line of sight.
Light emitted during one field of the PDP is basically composed of: signal components, for example, of 10 to 12 sub-fields each having a different gray value; and persistence components of fields subsequent to the 10 to 12 sub-fields. However, blue phosphors have an extremely short persistence time. Thus, the following description assumes that only the blue phosphors do not include any persistence component. (a) in FIG. 1 shows a time distribution of light emission during one field period of one white pixel including stationary red, green, and blue image signals each having 255 as an image value (hereinafter represented as red: 255, green: 255, and blue: 255). In other words, a red signal component 201 is followed by a red persistence component 204, and a green signal component 202 is followed by a green persistence component 205. In the case of a blue phosphor, only a blue signal component 203 emits light.
The integration on the retina is performed on the emitted light of red, green, and blue phosphors as shown in (b) of FIG. 1. In other words, the integration on the retina is performed on the red signal component 201 and the red persistence component 204 along a line of sight 206 that is fixed to obtain a red-signal-component integral quantity 207 and a red-persistence-component integral quantity 210 on the retina. Consequently, a human perceives the sum of these integral quantities as a red color through the sense of sight. Similarly, the integration on the retina is performed on the green signal component 202 and the green persistence component 205 to obtain a green-signal-component integral quantity 208 and a green-persistence-component integral quantity 211 on the retina. Consequently, a human perceives the sum of these integral quantities as a green color through the sense of sight. Finally, the integration on the retina is performed on the blue signal component 203 to obtain a blue-signal-component integral quantity 209 on the retina. Consequently, a human perceives the integral quantity as a blue color through the sense of sight.
Although the obtained integral quantities of the red, green, and blue signals are equal, a human perceives them as white. This is because emitted light includes the blue-signal-component integral quantity 209 greater than the red-signal-component integral quantity 207 and the green-signal-component integral quantity 208 by the red persistence component 210 and the green persistence component 211. In other words, although the red, green, and blue image signals have the same value, the blue signal component on the PDP has intensity of light emission higher than those of the red and green signal components.
Thus, when the line of sight is fixed, no motion blur occurs.
However, when the line of sight moves and phosphors including red and green persistence components emit light, motion blur occurs. Furthermore, when phosphors having no blue persistence component emit light to display an object, the color shift occurs due to a difference in a time distribution of light emitted from each of the phosphors.
FIG. 2 explanatorily shows integration on the retina for each color when a line of sight traces a white image signal in a pixel. This integration on the retina will be explained using FIG. 2.
(a) in FIG. 2 shows a time distribution of light of 2 field periods when a white dot (red: 255, green: 255, and blue: 255) in a pixel is horizontally displaced to the right in a black background (red: 0, green: 0, and blue: 0) at a predetermined velocity. However, there is no difference between light emission of one field period and the light emission in (a) of FIG. 1 despite the displacement operation. In other words, red signal components 301 and 306 are followed by red persistence components 304 and 309, and green signal components 302 and 307 are followed by green persistence components 305 and 310. In the case of a blue phosphor, only blue signal components 303 and 308 emit light.
(b) of FIG. 2 shows integral quantities for each color on the retina in the case of t=T to 2T (T represents one field period) when a line of sight is fixed (a line of sight 311). In this case, the integration on the retina is performed on the red persistence component 304 and the green persistence component 305 respectively in positions of integral quantities 312 and 313. Furthermore, the integration on the retina is performed on the red signal component 306 and the red persistence component 309 in an identical position to obtain integral quantities 314 and 317, respectively. Similarly, the integration on the retina is performed on the green signal component 307 and the green persistence component 310 in an identical position to obtain integral quantities 315 and 318, respectively. The integration on the retina is performed on the blue signal component 308 to obtain an integral quantity 316. As a result, only red and green persistence remain in the positions of the integral quantities 312 and 313, it causes color shift, and a human perceives it as yellow. However, since the color shift occurs in a very short period of one field period, the color shift poses almost no problem.
However, the motion blur occurs and causes a problem of the color shift to occur when the line of sight traces a white dot in the one pixel. This will be described with reference to (c) in FIG. 2.
(c) in FIG. 2 shows that integral quantities for each color on the retina in the case of t=T to 2T when the line of sight (line of sight 319) traces a white dot. Since tracing the dots continuously, the line of sight sequentially moves to the right according to the passage of time, as the line of sight 319. Thereby, integration on the retina is performed on each color along the line of sight 319. In other words, the integration on the retina is performed on the red signal component 306, the green signal component 307, and the blue signal component 308 to obtain integral quantities 320, 321, and 322, respectively. The integration on the retina is performed on the red persistence components 304 and 309 and the green persistence components 305 and 310 in the case of t=T to 2T to respectively obtain integral quantities 323 and 324 each having a geometry like a tailing. As a result, a human perceives the image as shown in (d) of FIG. 2. In other words, the signal components 320, 321, and 322 of each color on the retina are perceived as somewhat blue as shown by the integral quantity 325. Moreover, the persistence components 323 and 324 on the retina are perceived as a yellow tailing shown by the integral quantity 326. When a line of sight traces a moving object, integration is performed on several fields continuously. Thus, the motion blur and the color shift caused by the motion blur become more visible and the image quality is degraded subjectively.
As such, although only one white pixel originally is displaced, color shift occurs in a moving direction when a line of sight traces a moving object. The color shift causes image components to be perceived as somewhat blue and a persistence component to be perceived as yellow.
This is the principle of the motion blur and the color shift occurring when an object to be displayed with light emission of a phosphor including a persistence component is displaced.
The motion blur and the color shift in each pixel overlap with each other when there is a plurality of pixels, in other words, an image including the plurality of pixels.
FIG. 3 explanatorily shows integration on the retina for each signal component and each persistence component when a line of sight traces a white rectangle object in a gray background. (a) in FIG. 3 shows a state where the white rectangle object (red: 255, green: 255, and blue: 255) is horizontally displaced to the right at a predetermined velocity in the gray background (red: 128, green: 128, and blue: 128) using an image signal viewed on a PDP.
Next, (b) in FIG. 3 shows a time distribution of one field period of light emitted from one horizontal line that has been extracted from the image signal shown in (a) of FIG. 3. In other words, a signal component 401 emits light, and subsequently a persistence component 402 emits light. Thus, the persistence persists in the next field.
Then, a line of sight 403 subsequently moves to the right according to the passage of time since the line of sight continuously traces movement of the white rectangle object. The integration on the retina is performed along the line of sight. More specifically, the integration is performed on a component S1 included in the signal component 401 in a position P1 to calculate an integral quantity I1. Furthermore, integration is performed on: a component S2 included in the signal component 401 in a position P2 to calculate an integral quantity I2; a component S3 included in the signal component 401 in a position P3 to calculate an integral quantity I3; a component S4 included in the signal component 401 in a position P4 to calculate an integral quantity I4; a component S5 included in the signal component 401 in a position P5 to calculate an integral quantity I5; a component S6 included in the signal component 401 in a position P6 to calculate an integral quantity I6; a component S7 included in the signal component 401 in a position P7 to calculate an integral quantity I7; and a component S8 included in the signal component 401 in a position P8 to calculate an integral quantity I8. As a result, an integral quantity 404 of the signal component as shown in (c) of FIG. 3 is obtained from the signal component 401. Furthermore, integration is performed on: a component S11 included in the persistence component 402 in the position P1 to calculate an integral quantity I11; a component S12 included in the persistence component 402 in the position P2 to calculate an integral quantity I12; a component S13 included in the persistence component 402 in the position P3 to calculate an integral quantity I13; a component S14 included in the persistence component 402 in the position P4 to calculate an integral quantity I14; a component S15 included in the persistence component 402 in the position P5 to calculate an integral quantity I15; a component S16 included in the persistence component 402 in the position P6 to calculate an integral quantity I16; a component S17 included in the persistence component 402 in the position P7 to calculate an integral quantity I17; and a component S18 included in the persistence component 402 in the position P8 to calculate an integral quantity I18. As a result, an integral quantity 405 as shown in (d) of FIG. 3 is obtained from the persistence component 402.
Here, since only a white object is displaced in a gray background, other colors such as blue or yellow should not be perceived. As described above, white represented by signal components on the PDP is perceived as somewhat blue, persistence components are perceived as yellow, and consequently, a sum of these components are perceived as white. Thus, the integral quantity 404 of the signal components needs to be proportioned to the integral quantity 405 of the persistence components on each coordinate position. However, as shown in (d) of FIG. 3, the persistence component 405 has excess or deficiency (hereinafter referred to as motion blur component). In other words, a persistence excess amount 408 occurs in the vicinity of a region 406 where a value of a red or a green image signal is reduced from a previous field to a current field (hereinafter referred to as reduced intensity region) and the region is perceived as yellow. On the other hand, a persistence deficiency amount 409 occurs in the vicinity of a region 407 where a value of a red or a green image signal is increased from a previous field to a current field (hereinafter referred to as increased intensity region) and the region is perceived as blue.
This is the principle of the motion blur and the color shift.
Patent Reference 1 suggests a method for reducing color shift caused by the persistence excess in a vicinity of the reduced intensity region by generating a pseudo-persistence signal from a current field and adding the generated pseudo-persistence signal to the current field. The pseudo-persistence signal has a broken-line characteristic identical to those of the red and green phosphors with respect to a blue image signal.    Patent Reference 1: Japanese Unexamined Patent Application Publication No. 2005-141204